Pulsed-lasers can be switched between an inactive or "ready" operation mode and a pulse-drive operation mode by means of a gate or the like. In the inactive-mode the laser is held ready for use but does not deliver any laser radiation. Triggering the gate causes the laser to switch to the pulse-drive mode in which it can deliver an individual pulse or a series of pulses. In the ready-mode, the pump-light source keeps the gain-medium energized at a maximum (saturation) value. After the first pulse is switched, energy in the gain-medium is sharply depleted, generally almost to zero. Thereafter energy build up gain at a rate dependent on a characteristic time-constant of the gain-medium. If further pulses are delivered before the energy in the gain-medium has reached a value close to the maximum value, the result is a sawtooth-like temporal variation of the energy in the gain-medium, with peak values which are less than the maximum or saturation value. An effect of this is that the energy of the first pulse is increased over the energy of pulses which follow. The increase is greater the shorter the time-interval between pulses relative to the energizing time-constant of the gain-medium. This effect is undesirable in many applications of pulsed-lasers and can only be suppressed by controlling the first pulse in some way.
In U.S. Pat. No. 5,225,051 a pulsed-laser is disclosed in which the power of the pump-light source is reduced in the event that the time-interval between successive pulses exceeds a particular limiting value. In this way, the peak energy of the gain-medium is limited to a value about that which corresponds to the peak values in a continuing series of pulses.
A disadvantage of this prior-art pulsed-laser is that the pump-light source must be rapidly and precisely controlled over a wide range of power. Providing such control increases the technical complexity of the laser and, moreover, is only possible at all with certain types of pump-light source. In this prior-art laser, the pump-light source must be driven at a sharply reduced power. This can lead, with certain pump-light sources, to undesirable changes of properties of the pump-light source, for example, a change of wavelength in diode-laser pump-light sources. After a switch to pulse-drive mode, the pump-light source must first stabilize to a new drive-condition, whereby the first portion of a pulse-series or pulse-train delivered by the laser can be unstable.
There is a need to provide a pulsed-laser in which the energy of the first-delivered pulse of a series of pulses does not differ significantly from successive pulses in the pulse-series, while avoiding the disadvantage of the above-described, prior-art pulsed-laser.